DESCRIPTION: The proposed work attempts to define the pathway mediating neuromodulatory effects of natriuretic peptides which produce a variety of hypotensive effects including diuresis, vasodilation, and inhibition of both steroidogenesis and adrenergic neurotransmissions. Past work found natriuretic peptides to inhibit neurotransmission via "clearance" (ANP C) receptors coupling to a pertussis toxin sensitive process (that does not involve a reduction in cytoplasmic calcium concentrations. It is induced catecholamine release. The hypothesized pathway includes (ANP C) receptors interacting with GTP binding proteins to suppress phospholipase C activity, protein kinase C activity and catecholamine release. Experiments will be performed in a rat pheochromocytoma adrenergic cell line, PC12 cells. The PC12 cells allow monitoring of the complete sequence of proposed events (i.e., receptors, GTP binding proteins, phospholipase C activity, protein kinase C activity, and catecholamine release). The specific aims include: 1) assessing the contribution of [ANP C receptors to neuromodulatory effects of natriuretic peptides; 2) assessing the contribution of GTP binding proteins to neuromodulatory actions of natriuretic peptides; and 3) assessing the involvement of phospholipase C and protein kinase C in neuromodulatory DA release actions of natriuretic peptides. The first specific aim will examine effects of both ANP C receptor activation and ablation on subsequent events in the proposed pathway. The second specific aim tests for coupling of GTP binding proteins to the ANP C receptor, phospholipase C and subsequent events in the hypothesized pathway. The third specific aim tests whether suppressed phospholipase C and protein kinase C activities are essential for neuromodulatory influences of natriuretic peptides.] These results will impact on the natriuretic peptide field by identifying alternative signal transduction pathways to guanylyl cyclase activation, the pathway currently perceived to mediate all natriuretic peptide actions. The primary contribution will involve a critical assessment of the natriuretic peptide receptor involved in mediating neuromodulatory effects and the coupling of this receptor to GTP binding proteins. The proposed work will test if the (ANP C) receptor specifically mediates neuromodulatory actions of natriuretic peptides.